The present invention relates to an automatic gain control (AGC) circuit for use in the transmission and reception of burst signals in a time division multiple access (TDMA) system, or the like.
One of the systems used in satellite communication, and the like, is known as the burst communication system, in which a transmitting action is performed only when information is to be conveyed. This burst communication system has the advantages that the power consumption can be reduced and that the same satellite and the same frequency band can be used for communication between many different transmitting and receiving stations.
In a transmitter for the burst communication system, an AGC amplifier is used for keeping constant the variation of transmitting power which is caused by temperature fluctuation or by switching the transmission path. In a receiver, an AGC amplifier is used for keeping constant the variation of the reception input power, thereby stabilizing the demodulating action. It is customary in such an AGC circuit for burst signals to achieve AGC by the use of a negative feedback bias responsive to charging/discharging or time constant circuit having a peak holding function.
However, as will be described in detail below, a conventional AGC circuit for burst signals has the disadvantage that a change in burst time would invite a variation in the output power of the AGC circuit, so that it could not achieve its intended purpose to keep the output power constant. As a result, if the circuit is used in a transmitter, the transmitting power may vary; or, if it is used in a receiver, the input to the demodulator circuit may vary, to adversely affect its receiving function.